The present invention relates to a writable optical disc, and a reading system and a manufacturing method of the disc.
In a writable optical disc, information such as a synchronizing signal and address information (hereinafter called prepit information) for searching a position on the disc are previously recorded by laser cutting at a preformat stage in a manufacturing process. As one of methods of the preformat of the prepit information, a track (groove or land) on which information is written by a user is wobbled. In another method, prepits are recorded on the track.
However, in the former method, the track itself is wobbled in a waveform in right and left by a wobbling signal. Therefore, the magnitude of the modulation by the wobbling signal is limited to a small degree. As a result, the C/N decreases. Furthermore, since the interference of the adjacent tracks at the wobbling must be considered, pitch between the tracks can not be reduced. Consequently, the writing capacity of the disc is limited.
In the latter method, since the prepits are recorded, the space for writing the information is reduced. Therefore, the available efficiency of the disc is low.
An object of the present invention is to provide a writable disc in which the writing capacity of the disc is increased.
Another object of the present invention is to provide a reading system of the disc which can be effectively read out written information.
A further object of the present invention is to provide a manufacturing method of the disc where the disc is efficiently manufactured.
According to the present invention, there is provided a writable optical disc having an information writing track, and a guiding track for introducing a laser beam to the information writing track, characterized in that the guiding track has prepit information recorded thereon, the prepit information including at least address information of the optical disc.
The prepit information is recorded on the guiding track at a position where interference of adjacent guiding tracks with the prepit information is prevented. The information writing track is a groove track, and the guiding track is a land track.
In accordance with the present invention, a reading system for reading a writable optical disc having an information writing track, and a guiding track for introducing a laser beam to the information writing track is further provided. The reading system comprises a photodetector having two photodetecting elements divided by a first line optically parallel with a radial direction of the disc for detecting reflected light of a laser beam reflected from the information writing track, and prepit information extracting means for extracting prepit information recorded on the guiding track based on a difference signal between outputs of the divided two photodetecting elements.
The photodetector is further divided by a second line optically parallel with a tangential direction of the information writing track of the optical disc, and the difference signal is obtained from an output of a pair of photodetecting elements positioned on an inside portion of the second line and an output of a pair of photodetecting elements positioned on an outside portion of the second line for producing a tracking error signal.
Another reading system for reading a writable optical disc having an information writing track, and a guiding track for introducing a laser beam to the information writing track comprises a first photodetector having two photodetecting elements divided by a first line optically parallel with a tangential direction of the information writing track of the disc for detecting reflected light of a first laser beam reflected from the information writing track, a second photodetector having four photodetecting elements divided by a second line optically parallel with the tangential direction of the information writing track of the disc, and divided by a third line optically parallel with a radial direction of the disc for detecting reflected light of a second laser beam reflected from the guiding track, first difference signal producing means for producing a first difference signal based on a difference between outputs of the divided two photodetecting elements of the first photodetector, second difference signal producing means for producing a second difference signal based on a difference between outputs of a pair of photodetecting elements positioned at an inside portion and at an outside portion of the second line of the second photodetector, third difference signal producing means for producing a third difference signal based on a difference between outputs of a pair of photodetecting elements positioned on a portion at a reading forward direction side and at a reverse direction side to the reading forward direction of the third line of the second photodetector, tracking error producing means for producing a tracking error signal based on the first difference signal and the second difference signal, and prepit information extracting means for extracting prepit information on the guiding track based on the third difference signal.
The present invention provide a reading system for reading a writable optical disc having an information writing track, and a guiding track for introducing a laser beam to the information writing track wherein noises included in the prepit information is removed. The reading system comprises a photodetector having two photodetecting elements divided by a line optically parallel with a radial direction of the disc for detecting reflected light of a laser beam reflected from the information writing track, prepit signal producing means for producing a difference signal as a first prepit signal, from outputs of the divided photodetecting elements, added signal producing means for producing an added signal of outputs of the divided photodetecting elements, noise cancel signal producing means for producing a noise cancel signal based on the added signal, and noise extracting means for subtracting the noise cancel signal from the first prepit signal to produce a second prepit signal without noises caused by the added signal.
Another reading system for reading a writable optical disc having an information writing track, and a guiding track for introducing a laser beam to the information writing track comprises a photodetector having two photodetecting elements divided by a line optically parallel with a radial direction of the disc for detecting reflected light of a laser beam reflected from the information writing track, prepit signal producing means for producing a difference signal as a first prepit signal, from outputs of the divided photodetecting elements, noise cancel signal producing means for producing a noise cancel signal based on a laser beam for writing information on the information writing track, and noise extracting means for subtracting the noise cancel signal from the first prepit signal to produce a second prepit signal without noises caused by the writing laser beam.
There is further provided a method for manufacturing a writable optical disc having an information writing groove, a guiding land, and prepit information recorded on the land, the method comprising steps of performing a laser cutting to expose a resist coated on an original glass substrate by a laser beam modulated based on prepit information to be recorded on a land, developing the exposed resist, thereby forming a land and prepits on the land, performing electroforming to the developed glass substrate for producing a master stamper, performing electroforming to the master stamper for producing a sub stamper, and replicating an optical disc by using the sub stamper.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.